I am curious about the effectiveness of scalp tattooing among hair loss treatments.

I recently learned about scalp tattooing as a hair loss treatment. At first, I thought it was just a procedure where you tattoo the scalp, but it seems quite common. However, since I know absolutely nothing about this field, I have many questions. I am curious if the results of a scalp tattoo are barely noticeable even up close. Does the color change strangely or become too dark over time? When I think of hair loss treatments, I only think of hair transplants, so I am not sure exactly why people get scalp tattoos or what their effects are. Is it done as a second-best option when hair transplants are not possible or circumstances do not allow it? Or is it done because scalp tattooing has certain advantages?